The present invention relates to heat a sink for removal of heat from a heat source, in particular, from a semiconductor chip or a similar electronic or electric devices which are heated during the operation and are located in confined spaces.
Semi-conductor chip packages, which may contain a plurality of integrated circuits combined into a compact unit, become more complex and operate at higher frequencies. As a result, during operation they generate more heat. As a rule such devices are located In confined spaces from which the heat has to be removed. However, electronic devices can normally be heated to a predetermined limit. Heating above this limit may impair performance characteristics of the device and even lead to its damage. Moreover, long-term operation in a heated state, even at temperatures below the threshold, may drastically reduce the service life of the device.
Thus, in general, the component package configuration and construction are specifically designed to allow for maximized heat dissipation. Heat spreaders and heat sinks are employed in such electronic component packages to transfer heat to a moving air stream or on to another surface.
It should also be noted that a part of the heat flows from the chip to the ground plane of the PC board through the pins and the bottom side of the case, and will be partly carried away by convection to the entire PC board. As result, the temperature of the PC board increases for the following four reasons: 1) the PC board thin copper ground plane has high heat resistance; 2) the available ground plane size of copper is limited in dense PC boards; 3) the narrow and thin traces have high heat resistance; 4) other devices on same board might generate heat too, which can heat the device to higher temperatures.
In some IC devices, small part of the heat will be dissipated to the top side of the IC, as the heat resistance between the internal die and the top case Is fairly large. In this case the base part will be the dominant one for heat dissipation.
In order to enhance the heat-dissipation effect through a heat sink, some heat sinks are provided with an air funnel for directing the flow of air through the heat sink and between the heat-dissipating fins.
In modem heat-sink assemblies, the problems associated with limitations in connection with holes in the chip support members are solved with the so-called surface-mount technique, while the problems associated with automatic assembling are solved by the use of various snapping connections.
The surface-mount technique is based on the use of soldering. Pads on the circuit board are provided with a solder mount for the heat sink or a clip holding the heat sink. A circuit component is mounted to the heat sink and the component and heat sink are mounted to the board, the heat sink being mounted to the pads to dissipate heat from the circuit component attached thereto. In some cases, the heat sink or pads are connected to a ground plane in the circuit board to additionally dissipate heat from the circuit board. Heat-exchanging contact between the heat sink and the chip can be carried out through mechanical contact or through a heat-conductive medium that fills the space between the bottom of the heat sink and the facing surface of the chip. Furthermore, the heat is dissipated from all heated surfaces through a natural convection.
An example of a heat-sink assembly based on the use of a surface mounting technique is a device described in U.S. Pat. No. 4,625,260 issued in 1986 to W. Jordan, et al. The device comprises a heat-sink support, which is soldered to a PC board and has spring-loaded clips for detachably securing a heat sink. Although this device is suitable for automatic assembling in combination with the surface-mount technique, it has spring-loaded attachment of the heat sink, which is unreliable for use under conditions of shakes and vibrations.
Heat-sink devices are not necessarily surface mounted. For example, U.S. Pat. No. 5,386,144 issued in 1995 to P. Variot et al. discloses an electronic component assembly which comprises an electronic component package, a heat sink having an outwardly projecting latching members, and spring arms on the component package for resiliently clamping the latching members to the component package. The heat sink has a body configured and arranged to bear on the electronic component and mounts a latching member extending from the body and including a shank extending from the heat sink body having a latching flange at the distal end of the shank. A disadvantage of the invention disclosed in U.S. Pat. No. 5,386,144 is that it is applicable to component packages having a very specific configuration and therefore is not universal in its use. Another disadvantage is a complicated construction of the heat-sink attachment that requires the use of springing and latching members.
U.S. Pat. No. 6,075,699 issued in 2000 to W. Rife discloses a heat sink assembly installed above an electronic component for removing heat therefrom. The assembly includes a base member with downwardly directed legs, which have snapping ends for insertion into mounting holes formed on a support that mounts the electronic component. The base member has a central threaded opening for threadably receiving a heat sink to position in which the end of the heat sink is in flush thermal communication with the electronic component while the legs are secured within their respective holes in the electronic component. The device of U.S. Pat. No. 6,075,699 is designed for removal of heat only from the chip itself and cannot be used for cooling the surrounding lead wires and other electrical connections. This is because the heat is transferred to the heat exchanger only from the chip and cannot be efficiently transferred through the snapping ends of the attachment legs. Another serious disadvantage of the aforementioned construction is that it has a limited application and is suitable only to those designs, which allow holes in a chip-supporting member, which is not always the possible. Furthermore, in case of automatic assembling, threaded connection of the heat sink with the base member will slow down the assembling operation and will make it more complicated and expensive.
An example of a heat-sink assembly which can be used only with PC boards that allow holes in their structures is a device of U.S. Pat. No. 5,917,701 issued in 1999 to T. Solberg, which discloses a vertically-arranged heat-sink support structure that consists of a lower member and an upper member. The circuit board has a plurality of openings in a mounting surface thereof. The fastener includes a body having a main portion. A spring clip extends in a first direction from the main portion into the groove and is biased to engage the first and second surfaces of the heat sink. A plurality of latches on the spring clip engages the lock recesses when the spring clip engages the first and second surfaces of the heat sink. A plurality of anchor lugs extends in a second direction from the main portion, opposite the first direction, to be received in respective openings in the board to rigidly attach the fastener to the circuit board. Preferably, the anchor lugs are of differing lengths and configurations to permit assembly of the clip to differently sized circuit boards. Also preferably, engagement protrusions on the clip engage a concave surface on the heat sink.
An advantage of the assembly of U.S. Pat. No. 5,917,701 is that it is suitable for automatic assembling. However, this assembly requires a provision of holes in the PC board. A second disadvantage is a provision of spring-loaded clips, since with the lapse of time the clips may loose their resiliency, so that conditions of heat-conducting contact can be lost. Moreover, if the entire device operates under conditions of vibrations or shocks, the upper and lower parts of the heat-sink attachment can get loose and be completely disconnected.
It is an object of the present invention to provide a heat sink device which is suitable for automatic assembling, is simple and universal in construction, inexpensive to manufacture, does not use screws, ridge other threaded connections, or clips, removes heat not only from the chip but from the chip-supporting areas of the PC board, can be installed on a PC board without the use of holes in the PC board, allows to minimize the amount of parts in a heat-sink assembly by combining the base and the funnel into an integral unit made from a single workpiece, simplifies attachment of the heat sink to the base with the use of an automatic assembly machine such as a xe2x80x9cpick and placexe2x80x9d machine, and improves reliability of heat-transfer contacts in a heat-transfer chain of the assembly.
The heat-sink assembly of the invention is attached to the PC board with the use of surface mount technology. The assembly comprises a base part or a base member soldered to the PC board and a top part or a heat-sink member snapped-on through the central opening of the base member by irreversibly deforming bendable lugs which may have a radial or any other suitable shape. The bottom of the heat-sink member may be pushed down to physical contact with the top of the chip or to a position that leaves a space between the bottom of the heat-sink member and the top of the chip, so that the aforementioned space may be filled with a heat-conducting medium. It is an option to use the base part only. If necessary, a second heat-sink member of the same type, which could have different dimensions, can be soldered to the PC board side opposite to the chip. The heat sinks could be used with or without a fan.